Gas flow indicator



May 1s, 1943 c. H. PHI-:LPS

GAS FLOW INDICATOR Y miga Nov. 28, 1941 AAAAAAAAAAAAA "A INVENTOR,

Patented May 18, t 1943 UNITED stratesraren-r offre-liza Clyde `H. Phelps, Springeld, Ill., assigner to e Weaver Manufacturing- Coxnpany, Springfield, lll;a corporation of Illinois Anplicatinn- November '28, 194,11', SeriarNo. 420,850

(Cl. 7Bf-204)` S'Clairns.`

The present invention relates to novell features of benefit in'` gas-flow indicators of the electricaltype, and it concerns more particularly, but not `necessarily exclusively, appliances of this character for usel in the fieldl where minute `flowl or lowfpressure indications are required, such, for instance, as the determination of stack or' ue draft, fire-box pressure, and in other applications wherein pressure, either superatmospheric or subatmospheri'c is encountered in a range'f'rom .001 to .11 of water-column.

'Eheusual-` practice influeand stack draft measurements involves theempleyment `of afiuid operated, inclined glassetube, which must be carefully; leveled# and main-tained at a substantiallyconstant temperature and which isdifcult- .to use where-the` pressure is: veryilow' due to the fact that' there is' littlev change in' liquid-level with a pressure as small as that speciecl above.

Nickel, copper, platinum and some other metals change their resistance materially to the passage of electricfcurrents vwith modification of their temperatures, whereasl some alloys, suchl as Inanganin,` have substantially unyarying resistance, over comparatively wide temperature ranges, and thisinvention employs the combina.- tiono-f these extremes in an electrical-circuit whereby preheated, air or gas, ispassed over a resistor the resistance of which changes ing proportion to itsternperature, thereby providing, a sui-table means of indication of the higher Aheat or temperature of such resistance due: to the transfer of heat from the preheatedsource, `the galvanoxneter of the Wheatstonefbridge. circuit in which the` resistances are; included. being calibrated;` in terms. of flowor pressure causing the flow. i

Statedpsornewhatotherwise, the present invention. concerns impr,oyernents` in draft-gauges in particular with means to. show the directionv of new and to indicateV whether positive pressure or vacuum is encountered, an example of such a test being means to denote the condition of' a fire-box of a-n ordinary heating-plant to determine if an adequate draft exists, or a positive pressure is present, the latter if occurring tending to cause combustion products to escape through any existing cracks in such a furnace andto iind their way into the hot-air stream from the furnace to the rooms heated, and, as combustionproducts often contain carbon-monoxide, which can have a deadly effect, such a situation should not be permitted to exist.

In order te permit those skilled in this art-V to fully understand the invention, acurrent em bodimentr of the same has been illustrated in de'- tai-l in the accompanying Vdra-wing in which the single ligure shows: the circuit-connections and illustrates the novelappliance in central, vertical Section By reference to suchV drawing, it will be readily perceived thatthe. well-known Wheatstone-bridge electric-circuitincludes four resistors Rie-I, R2, 1%-3 and Rf-4' as its like number of arms, the battery lll, for instance, of suitable voltage, supply-ing currentthrough an adjustable rheostat Il to` the circuit by connections` I2 and` |13j to1 the points between theresistances R-l and Pew-3V on the one ha-ndandl R-Z and Ri--A on the other hand', an appropriately-graduated galvanometer Hi` beingV joined to the circuit between the resistances' Pff-3, and; R-l and' between` the resistances R-l and Etf-2. as; is4 common practice in the employmentof a system of that type.

The two resistors R-3 and R-4 are composed of a material which does not materially change its resistance with alterations in temperature, whereas the resistors Rr-I and. R-2 are of a material which has a high temperature resistance coeiii'cieht and Will therefore modifytheir resistances readily'with temperature changes.

A fifth resistor R- is of substantially nonchangeable resistance and is electrically heated toa practicallymniform or constant temperature by its inclusion in the independent electric-cir--y cuit `l-supplied by a heating electric-current from a source I6 of' direct-current or alternating-cnn rent of. electricity. of appropriate voltage.

The three resistors. RFI', R-5I and Rf2 are mounted in a single, metal cell-block HJ common to all three and composed of a metal or other material having high thermal conductivity, such, for

example, as copper, aluminum or the like, in order to have a tendency to equalize the4 temperature throughout the. entire. block.

Such` block has three equal-length cylindrical chambers or holes i8., I9, 2l through it in the same general plane, the two end` ones` I8 and 2l, in the present case, being of equal caliber, whereas the central one I9 is of somewhat larger diameter.

Each such hole is lined with a tube 22 of a material of low thermal-conductivity, such, for instance, as fiber or Bakelite, and while the cellblock I1 hasI practically-uniform heat-distribution throughout, the chambers or compartments Within two of the tubes are'insulated from the heated central resistor R-5 whose associated tube or encasing lining 22 is desirably somewhat thicker than the other two.

Each end of each such hollow cylindrical liner 22 has an electrical-insulation sleeve 23 fitted snugly therein, such sleeve having an enlarged head outside of the block I1 and overlying the adjacent end of the tube and an adjoining portion of the block Il, each such sleeve accommodating a hollow rivet 24 within it, the outer end of which is closed by an electric-terminal 25. Each of the three resistors R-I, R- and R-Z has its opposite ends connected, as by solder or otherwise, to the two terminals 25, 25 of its corresponding chamber formed by the liner and its end closures.

From the drawing, it will be seen that -a pipe or conduit 26 connects from the outside of the block il with one end of the chamber housing resistor R-2, that a port 21 connects the opposite end portion of such chamber or cell with the co1'- responding end of the middle compartment accommodating resistor R-5, that the other end portion of such central chamber is connected to the adjacent end of the third cell encasing resistor R-I by a port 28, and that the other end of such latter cell is fitted with a pipe or tube 29 opening exterierly of the block.

Thus the three chambers are joined together in 4series relation from the one pipe 26 to the other 29, with the uniformly and continuously heated resistor R-5 occupying the intermediate chamber or cell.

Assuming that the parts are coupled up as illustrated with direct electric-currents supplied to the Wheatstone-bridge part of the system and that an electric-current has been applied to the resistor Rfto bring it up to its predetermined heat limit and is maintaining it continuously and unvaryingly thereat, the galvanometer will have a zero reading with no air or gas ow through the connected cells of the block.

If now a source of gas-pressure is connected to the interior of the block as, for example, through the pipe 26, the air-stream passes through the chamber of resistor R-2 around the latter, then through the middle chamber Where fit is heated by the resistor R-E, and then as it flows through the third chamber, it transfers heat, which it has absorbed in the middle chamber, to the resistor R-I increasing the resistance thereof, and the amount of this resistance-change or unbalance of the bridge-circuit is indicated on the associated galvanometer which may be calibrated in the desired units of pressure or flow, it being apparent that the amount of resistance alteration will depend upon the rate of flow of air` through the chambers and this, of course, is proportional of the pressure under investigation.

If the direction of flow through the combined or affiliated chambers were reversed, as by connecting the source of pressure with the pipe 29, instead or" to the pipe 26, or by connectingpipe 26 to a source of subatmospheric pressure, the accompanying reverse flow of air through the chambers or cells would cause heat-units to be conveyed from resistor R-5 to resistor R-2, thus shifting the galvanometer-needle in the opposite direction an amount to indicate the direction of flow and its degree.

If desired, the galvanometer may be graduated to show the velocity of the flow.

Again, if both pipes 26 and 29 are simultaneously associated with different pressures, the galvanometer can be used to indicate the dierential directional ow.

The multiple-resistor unit herein illustrated and described is simple and rugged in structure, is relatively inexpensive to manufacture, is reliable in operation, and is unlikely to become damaged or injured in ordinary service.

The source of current I6 may be of three volts or any other suitable amount, each of the resistors R-I, R-Z, .Rf-3 and R-4 may be of about 25 ohms each, the galvanometer may be one of approximately 25 ohms, and the resistor R-5 may be of 50 ohms, but, of course, it will be understood that they are subject to change as occasion dictates, and it is to be remembered that the details of structure and arrangement of parts is presented by Way of example and changes and modifications may be resorted to without departure from the scope of the invention as defined by the appended claims.

I claim:

1. For use in a gas-now indicating-system, a resistance-device including in combination a member having first, second and third chambers connected together in series relation in that order whereby gas may flow through said series in either direction, said member having an external port for each of said rst and third chambers, and rst, second and third electrical-resistances in said respective chambers, said rst and third resistances being adapted for electrical connection in a Wheatstone-bridge system, said second resistance being adapted for inclusion in a separate heating electric-circuit, the combination of novel features being that said member is of relatively-high heat-conductivity, said chambers are r elongated and are substantially parallel with one another, said ports are at opposite end portions of said rst and third chambers, the other end portions of said rst and third chambers are connected to the opposite end portions of said second intermediate chamber, said resistances are disposed lengthwise in their respective chambers, and all in combination with heat-insulating linings in said chambers.

2. The combination of novel features set forth in claim 1 including the additional novel feature that the insulating-lining of said second-chamber is of greater insulating-capacity than the linings of said rst and third chambers.

3. The combination of -novel features presented in claim 1 including the additional novel feature that said chambers extend entirely through said member, in combination with `closures for the ends of said chambers having accessible electricterminals for said resistances.`

CLYDE H. PI-IELPS. 

